1. Field of the Invention
The invention is directed to the field of pressing of powders to make inserts.
2. Description of Related Art
Powder metallurgy has become a viable alternative to traditional casting and machining techniques. In the powder metallurgy process, one or more powder metals and/or ceramics, with or without a fugitive binder, are added to a mold and then compacted under very high pressures, typically between about 20–80 tons per square inch. The compacted part is ejected from the mold as a “green” part. The green part is then sintered in a furnace operating at temperatures of typically 1100°–1950° C. The sintering temperature depends upon the composition of the powder mixture. For example, cemented carbide and cermets are typically sintered at 1350°–1450° C. while ceramics are typically sintered at 1500°–1950° C. The sintering process effectively welds together all of the individual powder grains into a solid mass of considerable mechanical strength with little, if any, porosity. The powder metallurgy process can be generally used to make parts from any type of powder and sintering temperatures are primarily determined by the temperature of fusion of each powder type. Powder metallurgy parts have several significant advantages over traditional cast or machine parts. Powder metallurgy parts can be molded with very intricate features that eliminate much of the grinding that is required with conventional fabrication. Powder metallurgy parts can be molded to tolerances within about four or five thousandths of an inch, a level of precision acceptable for many machined surfaces. Surfaces which require tighter tolerances can be quickly and easily ground since only a small amount of surface material need be removed. Surfaces of powder metallurgy parts are very smooth and offer an excellent finish which is suitable for bearing surfaces.
The powder metallurgy process is also very efficient compared with other processes. Powder metallurgy processes are capable of typically producing between 200–2,000 pieces per hour, depending on the size and of the degree of complexity. The molds are typically capable of thousands of service hours before wearing out and requiring replacement. Since almost all of the powder which enters the mold becomes part of the finished product, the powder metallurgy process is about 97% material efficient. During sintering, it is only necessary to heat the green part to a temperature which permits fusion of the powder granules. This temperature is typically much lower than the melting points of the powders, and so sintering is considerably more energy efficient than a comparable casting process.
In spite of the many advantages of powder metallurgy parts, the fabrication of powder metallurgy parts suffers from certain drawbacks. Powder metallurgy parts are molded under high pressures which are obtained through large opposing forces that are generated by the molding equipment. These forces are applied by mold elements which move back and forth in opposing vertical directions along a pressing axis. The powder metallurgy parts produced thereby have previously necessarily had a “vertical” profile. Since mold elements move back and forth in opposing vertical directions, powder metallurgy parts formed with transverse features, i.e., holes, grooves, undercuts, cross-cuts or threads, would inhibit mold release and therefore these features would not be pressed into the green part. Such profile features then required a secondary machining step which added greatly to the cost of the part and creates an economic disincentive to fabricate parts using powder metallurgy.
A method and apparatus are desired capable of effectively imparting a through hole with or without a counterbore through a cutting insert using powder pressing techniques.